There are mainly four error recovery strategies : Panic mode Phrase level recovery Error production Global generation Panic Mode In this method on discovering error, the parser discards input symbol one at a time. This process is continued until one of a designated set of synchronizing tokens is found. Synchronizing tokens are delimiters such as semicolon or end. These tokens indicate an end of the statement. If there is less number of errors in the same statement then this strategy is best choice. Phase Level Recovery In this method, on discovering an error parser performs local correction on remaining input. The local correction can be replacing comma by semicolon, deletion of semicolons or inserting missing semicolon. This type of local correction is decided by compiler designer. This method is used in many error-repairing compilers. Error Production If we have good knowledge of common errors that might be encountered, then we can augment the grammar for the corresponding language with error productions that generate the erroneous constructs. Then we use the grammar augmented by these error production to construct a parser. If error production is used then, during parsing we can generate appropriate error message and parsing can be continued. Global Correction Given an incorrect input string x and grammar G, the algorithm will find a parse tree for a related string y, such that number of insertions, deletions and changes of token require to transform x into y is as small as possible. Such methods increase time and space requirements at parsing time. Global correction is thus simply a theoretical concept.
